1. Field of Invention
This invention relates to an image processing technique depending on changes of an optical system of a projector.
2. Description of Related Art
Projectors can be broadly classified into two categories: data projectors and video projectors, depending on their intended use. Classifying projectors therefore requires definite performance.
Data projectors project an image based on image signals received from an information terminal, such as a personal computer. Data projectors are typically used for presentations in well-lighted places, such as conference rooms and lecture halls, where brightness is important for a projected image. On the other hand, video projectors project a screen image of TV or a movie based on screen image signals received from an AV device. Video projectors are typically used for watching a movie in dark places, such as less-illuminated rooms, where picture quality including color balance or contrast is more important than brightness.
Various types of discharge lamps, such as ultra-high pressure mercury lamps, metal halide lamps and xenon lamps are generally used to provide illumination for projectors in terms of keeping high color rendering properties and high luminance. FIG. 10 is a graph that shows an emission spectrum of an ultra-high pressure mercury lamp. Projectors divide illumination into three colors; red light (R), green light (G) and blue light (B), which are modulated by light valves respectively, thereby projecting an image. Illumination can be utilized when it is divided into, for example, blue light in 400-500 (nm) wavelength range, green light in 500-600 wavelength range and red light in 600-700 wavelength range.
Projectors can be generally used as data projectors. Illumination that includes green light with high visibility can be used to enhance brightness of the projected image, which loses color balance between R, G and B.
Color balance adjustment in a projector that is used as a video projector can be performed by setting the tone value of the image data with regard to green light to, for instance, 0.8 times stronger than that used for a data projector. Namely, color adjustment can be achieved by weakening the strength of green light due to the drive of a liquid crystal panel (hereafter xe2x80x9cLCPxe2x80x9d), as shown in a dashed line in FIG. 10.
However, projectors that use an LCP as a light valve have not sufficiently attained a high level contrast ratio for the projected image in terms of the above-mentioned color balance adjustment. The contrast ratio is represented in the ratio between the brightness of the all-white-image and all-black-image.
FIG. 11 is a chart that shows the relationship between an input tone value and the brightness in projecting a gray color image where input tone values of R, G and B are equivalent. A solid line L1 shows the relationship between the input tone value and the brightness without the above color balance adjustment, and a dashed line L2 shows this relationship with the color balance adjustment. The contrast ratio without the color balance adjustment is represented by B1/B0, and B2/B0 represents the contrast ratio with the color adjustment. As shown in FIG. 11, in the above-mentioned adjustment, the brightness for an all black image remains in B0, though the brightness for an all white image decreases from B1 to B2 due to the characteristic of an LCP that luminance barely passes light valves even when all light valves are closed to project all black image (refer to a chain double-dashed line in FIG. 10). The contrast ratio thus decreases in the above-mentioned adjustment.
Accordingly, it has been difficult to achieve both the preferable color balance adjustment and the preferable contrast ratio at the same time.
Furthermore, the color balance adjustment has not been efficient for a black or a low tone image. There is a slight difference in the brightness between a black image that is projected with the color balance adjustment and such a projected image without the adjustment. Utilizing a lot of green light illumination has caused black images to be projected in a greenish gray color.
The present invention thus provides a technique of enhancing picture quality of an image projected by a projector.
At least part of the above and the other related advantages are attained by a projector with the following construction. The first embodiment of the projector includes: an image processing module that performs image processing with regard to an input original image data; an image generating module that generates an image based on an image data that is provided with the image processing; a projection optical system that projects an image generated by the image generating module using illumination light that includes specific emission spectrum; and an optical filter that is detachable and weakens at least part of spectral intensity in a wavelength range among an emission spectrum included in the illumination light, which affects the projection of the image. The image processing module performs the specific image processing in response to the changes of the spectral intensity caused by putting on/taking off the optical filter.
As described above, the color balance adjustment for a projected image is performed through the process of image processing in a projector that uses an LCP as a light valve, which causes low contrast ratio. The projector of the present invention has a detachable optical filter in order to weaken at least part of the spectral intensity. Using such an optical filter enables color balance adjustment for the projected image, and reduces or prevents low contrast ratio because that reduces the brightness for black color in the projected image as well as other colors. The optical filter can be removed from a projection optical system when brightness is more important than color balance.
In the projector of the present invention, because spectral intensity in projection light, which affects projection of the image, is different when the optical filter is attached compared to when it is not attached, the color balance of the projected image is different when the optical filter is attached compared to when it is not attached. The image processing module in the projector enables the adequate image processing, with regard to the original image data in response to the changes of spectral intensity in projection light, depending on the optical filter status, whether attached or not, thereby achieving both preferable color balance and preferable contrast ratio at the same time and enhancing picture quality of the projected image.
In the first embodiment of the present invention, the image processing may be any of diverse image processing techniques. It is, however, preferable that the specific image processing is color adjustment.
This procedure desirably enhances color reproducibility in the projected image.
In the first embodiment of the projector, it is preferable that the wavelength range affecting projection of the image responds to red light, green light and blue light, and that the optical filter has the highest reducing rate of spectral intensity in the wavelength range corresponding to green light.
Hereinafter, xe2x80x98reducing rate of spectral intensity in wavelength range corresponding to green light is the highestxe2x80x99 indicates that reducing rate of spectrum strength in wavelength range corresponding to green light is the highest among the projected light emitted from the projection optical system, which is not caused by characteristics of the optical filter.
In general, illumination light from a projector that uses an LCP as a light valve becomes greenish. Reducing spectral intensity with regard to green light enables effective color balance adjustment with high contrast ratio, and reduces or prevents the projected images in black or low scale from being greenish.
In the first embodiment of the present invention, the image processing module includes: a memory module that stores parameters used for the image processing in relation to the optical filter; a specific information input module that inputs specific information to identify the optical filter; and an image processing controller in order to select the parameters based on the specific information.
xe2x80x98Parameters used for image processingxe2x80x99 include a look-up table and a function showing the relationship between input tone values of the image data and output tone values for the image generating module. Such parameters used for the image processing are not restricted to parameters for the color adjustment. As xe2x80x98specific informationxe2x80x99, for example, the model numbers of the optical filters may be available. In the projector, the optical filter is selected with specific information, which enables adequate image processing.
In the projector, specific information may be manually input. It is, however, preferable that the image processing controller select the parameters based on specific information obtained from the specific information module of the optical filter, which stores the specific information.
The specific information input module thus automatically obtains the specific information, and the image processing controller selects the parameters based on the obtained information, which enhances the convenience of the projector. An IC chip and an electrode arranged uniquely in each optical filter can be used as the xe2x80x98specific information modulexe2x80x99.
In the first embodiment of the projector, the optical filter may be detachable to some portions in the projection optical system, for example, inside of the projector, according to its characteristic. It is, however, preferable that the optical projection system have a projection lens, and the optical filter can be attached to exterior of the projection lens.
The inside structure of the projector may thus be simplified, and the optical filter may be put on or taken off by the user easily.
In general, the above-mentioned image processing is available in terms of the specific image processing in response to the changes of optical characteristics in the projection optical system. Such process is applicable for the projector that is capable of putting on and taking off various projection lenses, such as a super-wide-angle lens and a telescopic lens, and other optical components.
In the second embodiment of the projector, a projector that projects an image includes: an image processing module that performs an image processing with regard to an input original image data; an image generating module that generates an image based on an image data that is provided with the image processing; a projection optical system that projects an image generated in the image generating module; and an optical component that is detachable from the image generating module, which enables the change of optical characteristics of the projection optical system. The image processing module performs the specific image processing in response to the change of optical characteristics caused by putting on/taking off the optical component.
This application enables adequate image processing for the original image data in response to the changes of optical characteristics in the projection optical system.
In the second embodiment of the projector, the image processing may be any of diverse image processing techniques. It is, however, preferable that the specific image processing be sharpness adjustment.
The optical components changing the range of the projection may be a projection lens, such as a super-wide-angle lens. Changing the projection lens may be performed based on changing the distance between the projector and the screen, which affects the degree of preferable sharpness adjustment when the projected range or the focused distance is changed. The projector enables adequate sharpness adjustment in response to the changes of optical characteristics in the projection optical system when changing an optical component, such as the projection lens.
In the second embodiment of the projector, the image processing module includes: a memory module that stores parameters used for the image processing depending on the type of the optical component; a specific information input module that inputs specific information to identify the optical component; and an image processing controller in order to select the parameters depending on the specific information.
This application enables the identification of the optical component based on the specific information, thus performing efficient image processing. The parameters used for the sharpness adjustment and other image processing can be used as the xe2x80x98parameters used for the image processingxe2x80x99.
In the projector, specific information may be manually input. It is, however, preferable that the image processing controller select parameters based on specific information obtained from a specific information module of the optical component, which stores the specific information.
The specific information input module thus automatically obtains the specific information, and the image processing controller selects the parameters based on the obtained information, which enhances the convenience of the projector.
The application of the present invention is not restricted to the projector. There are, however, a diversity of other applications of the present invention, such as an image processing method, a computer program providing such a method, a recording medium in which such a computer program is recorded, and a data signal including such a computer program and being embodied in a carrier wave, for example. The various additions and modifications described above are applicable to any of these embodiments.
When the technique of the present invention is embodied by any of the computer program or the recording medium in which such a computer program is recorded, the computer program may be the whole program for driving the image processing apparatus or the projector or only the partial program for attaining the characterized functions of the present invention. Typical examples of the recording medium include: flexible disks, CD-ROMs, magneto-optic discs, IC cards, ROM cartridges, punched cards, prints with barcodes or other codes printed thereon, internal storage devices (memories like a RAM and a ROM) and external storage devices of the computer, and a variety of other computer readable media, for example.